Process for manufacture of heavy aromatic solvent



United States Patent O 3,324,029 PROCESS FOR MANUFACTURE OF HEAVYAROMATIC SOLVENT Laurence F. King, Mooretown, Ontario, and Clellie T.

Steele, Sarnia, Ontario, Canada, assignors to Esso Research andEngineering Company, a corporation of Delaware No Drawing. Filed Sept.23, 1963, Ser. No. 310,894 8 Claims. (Cl. 208-97) This invention relatesto the production of improved heavy aromatic solvents. Moreparticularly, it relates to the production of a heavy aromatic solventwhich is superior to other oils in respect to vital properties such asodor.

Aromatic hydrocarbon fractions of 350-550 F. boiling range find wide useas solvents for insecticides such as DDT, aldrin and dieldrin.

Gas oil fractions recovered from steam cracked products are potentiallyuseful as heavy aromatic solvents. However, for many agricultural uses,the color, sulfur content and odor of steam cracked gas oils leave muchto be desired. Hyd-rofining and rerunning give improvement in color andsulfur but odor is deficient, probably because of heavy feed olefinswhich are very difiicult to hydrogenate with cobalt molybdate catalyst.

According to this invention a process is disclosed for treating overheadmaterial from the flashing of aromatic t-ar after the tar has been heatsoaked or destructively distilled. During this process, most of theolefins and other contaminants are thermally cracked and removed in thefront ends, resulting in considerable color and odor improvement. A350-550 F. boiling point heart out of the overhead from a heat treatedtar is hydrofined and the hydrofined distillate is rerun to produce animproved heavy aromatic solvent. In some cases the hydrofined distillatedoes not require 'rerunning. However, for best color and backendfractionation, it is preferred to distill or rerun it in vacuo to about90% overhead whereby most of the color bodies remain in the bottoms.

The aomatic tar feed needed to produce the solvent is obtained fromsteam cracking a gas oil or a mixed gas oil-naphtha. Traditionally, thistar was looked upon as a waste product and was only utilized as a lowgrade dark resin, or, more commonly, as bunker fuel. The steam crackingprocess is well known and involves cracking a 'gas oil having an initialboiling point between about 400 and 525 F. and a final boiling pointbetween about 750 and 825 F. in the presence of about 60-85 mol. percentof steam; at a coil outlet temperature between about 1200 and 1450 F.and immediately quenching with an oil having a boiling range betweenabout 500 and 675 F. to a temperature of about 540-560 F. The gas oilfeed has an API gravity of about 20 to 25, mo-l. weight of about 210 to270, weight percent aromatic rings of about 10 to 15 and weight percentnaphthenic rings of about 30 to 40.

The gaseous steam cracked products containing hydrogen, saturatedhydrocarbons, olefins, diolefins, etc., are taken overhead and theliquid hydrocarbons are fractionated to separate an aromatic gasolineboiling between about 100 and 460 F., and a higher boiling aromaticfraction boiling between about 370 and 570 F. which may be in partrecycled to the quench zone of the steam cracking unit. The amount ofresidual aromatic tar obtained is about vol. percent to 25 vol. percentof the feed and has an initial boiling point above about 500- 600 F.,and a 50% boiling point between about 700 and 800 F.

The aromatic tar thus obtained is then subjected to heat soaking.Temperatures which will be satisfactory fo-r heat soaking are between700 and 1000 F. and preferred 3,324,029 Patented June 6, 1967temperatures should be between 800 and 900 F. Pressure may vary between150 and 300 p.s.i.-g. with about 200 p.s.i.g'. being preferred. Spacevelocities will vary with the unit. For a 700 cc. capacity continuouspilot plant space velocities between 0.5 and 8.9 v./v./hr. volume ofliquid oil per volume of reactor space per hour are satisfactory.Periods of time for the heat soaking may range from a fe-w minutes to 5hours depending on the temperature with about 2 hours being preferredfor the range of 800-900 F.

Following the heat soaking, the tar is flashed. The flashing proceduremay be either vacuum or atmospheric. If atmospheric flashing isutilized, the tar is at a temperature of about 700-900 F., preferably at850-860 F. maximum or final temperature. Flashing pressure is generallyatmospheric but may be between 15 and 30 p.s.i.g. if desired and in thismanner an overhead hydrocarbon stream and -400 F. softening point pitchas bottoms is obtained. Flashed vapors are condensed and a 350- 550 F.boiling point fraction is recovered. The flashed distillate is passed toa hydrofiner.

An alternative route to flashing for obtaining this 350- 550 F. fractionis by destructive distillation of the aromatic tar obtained from steamcracking. The destructive distillation is carried on in the absence ofair and with pot temperatures varying from ambient to about 900 F. asthe distillation proceeds, with about 850-875 F. final pot temperaturebeing preferred for atmosphere pressure operation. Atmospheric flashing,or destructive distillation, may be practiced in lieu of heat soakingrather than as a second step.

In either case, the 350-550 F. fraction is then passed to a hydrofiner.Temperatures within the hydrofiner may be in the range of 500-800 F.,preferably a temperature of about 625 F. is utilized. Pressures of100-3000 p.s.i.g. may be utilized; a preferred pressure would be in therange of 200-1000 p.s.i.g. Feed rate may vary between l-3 v./hr./v.(liquid) volume of liquid oil per hour per volume of catalyst, dependingupon operating conditions. Hydrogen is used at a rate of 500-1000s.c.f./b. of feed.

The hydrofining catalyst consists chemically of cobalt oxide andmolybdenum oxide possibly combined as cobalt molybdate on a solidadsorbent carrier and can be purchased commerically. The carrier may beselected from many materials such as adsorptive alumina, bauxite, silicagel, clay, hydrogen fluoride promoted alumina and the like, which areusually employed for thi general purpose. A material which isparticularly preferred as a carrier, however, is alumina. It ispreferred that this catalyst contain about 2-5 wt. percent cobalt oxideand 8-15 wt. percent molybdenum oxide. About 3.6 wt. percent cobaltoxide and 12.5 wt. percent molybdenum oxide have been found to beespecially effective.

The catalyst, as it is employed in the present invention, may be in theform of a fixed bed, a fluidized bed or a moving bed.

Example 1 In a specific embodiment of this invention a hydrofineddistillate from heat soaked aromatic tar was produced. The tar wasobtained as bottoms from cracked products obtained by steam cracking a60-40 gas oil-naphtha at a temperature as set forth hereinafter and at40-43% conversion to C and lighter.

Characteristics of the tar were as follows:

Inspections of tar:

Gravity, API 4.0 Flash pt., F. 320 V./210 SSU 213 Carbon, percent by wt90.4

Residence time seconds about 3 Pressure, inlet p.s.i.g 80 Product yield,wt. percent:

Ethylene 25-27 Propylene 2021 Butylene Butadiene c -200 F. 13 200400 F.l3 Tar, vol. percent 7-11 The tar was then heat soaked at a temperatureof 850 F. and at a feed rate of 1.0 v./v./hr. (cold liquid feed).Pressure was maintained at about 200 p.s.i.g. The heat soaked productwas then flashed at 100 mm. to give a 430540 FVT distillate. Theresulting distillate was hydrofined over a cobalt molybdate catalyst.

Hydrofining was conducted at a temperature of 625 F. and at a pressureof 250 p.s.i.g. The feed rate was 0.5 v./v./hr. and hydrogen used was500 s.c.f. H /bbl. of feed. The hydrofined distillate was rerun ordistilled to recover a distillate (up to 90 vol. percent) having aboiling range of 420552 F. The distillate obtained was lye washed with15 volume percent of Baum caustic to remove traces of hydrogen sulfideremaining from the hydrofining step, and finally water Washed with about3 volumes of water per volume of distillate.

The final distillate comprises the improved heavy aromatic solvent ofthe present invention and has the characteristics given in Table I. Theimproved heavy aromatic solvent is compared with a commercial productdesignated as such in Table I.

TABLE I.INSPECTIONS OF IIEA\Y AROMATIC SOLVENT Mixed Aniline Pt. F 76 67Pour Pt. F 80 -55 ASTM Distillation:

IBP, 370 460 420 5% 400 478 430 10%... 415 .83 440 50% 450 505 488 90%500 535 520 95% 525 454 539 F.B.P 550 560 552 Additionally, in an odortest by a 20-member panel, the distillate or solvent from the heatsoaked tar was rated at +0.40 and the commercial solvent at -0.29. Theneeded difference for significance at the 95% confidence level is .25.Consequently, the distillate from the heat soaked tar scoredsignificantly higher on the odor test. The distillate from the heatsoaked tar also had a somewhat higher pour point, i.e. 25 F. higher butboth were so low that the difference is immaterial.

Thus, as illustrated by Table I, without the benefit of rerunning duringhydrofining, the tar showed improveent, the benefits would be increasedby rerunning.

In solvency, the distillate or improved solvent of the present inventionis significantly better than the more expensive commercial aromaticsolvent. This is shown in Table I by the lower mixed aniline point (67vs. 76 F.). The improved solvent also has a higher solvency for DDT at74 F. (40 vs. 35 grams/ grams solution dissolved at the saturationpoint) as compared to the commercial solvent. This is the most importantcriterion of all from the viewpoint of insecticide manufacturers. Thehigher solvency is due to formation of condensed aromatic ringstructures which have high solvency for insecticides.

What is claimed is:

1. A process for producing a heavy aromatic solvent having improved odorand superior solvency character istics which comprises steam cracking agas oil whereby an aromatic tar is produced, said tar having a boilingpoint above about 500 F., heat soaking the said aromatic tar, flashingthe heat soaked tar, recovering a 350 t 550 F. boiling point fractionand catalytically hydrotreating said 350 through 550 F. fraction wherebyan improved solvent is produced.

2. The process of claim 1 wherein the said heat soaking takes place at atemperature between about 700 and 1000 F.

3. The process of claim 1 wherein said hydrofining takes place over acobalt molybdate catalyst.

4. The process of claim 1 wherein said heavy aromatic tar has a boilingpoint above about 600 F.

5. A process for producing a heavy aromatic solvent with improved odorcharacteristics as well as improved solvency which comprises steamcracking a gas oil having an initial boiling point between 400 and 525F. and a final boiling point between 750 and 825 F. whereby an overheadfraction and a residual aromatic tar are obtained, heat soaking saidaromatic tar at a temperature between 700 and 1000 F., recovering a 350to 550 F. fraction from said heat soaked tar and catalyticallyhydrotreating said 350 to 550 F. fraction in order to produce animproved heavy aromatic solvent.

6. The process of claim 5 wherein said heat soaked tar is flashed inorder to recover said 350 to 550 P. fraction.

7. The process of claim 5 wherein said heat soaked tar is subjected todestructive distillation in order to recover said 350 to 550 F.fraction.

8. The process of claim 5 wherein said hydrofining takes place over acobalt molybdate catalyst.

References Cited UNITED STATES PATENTS 2,608,522 8/1952 Niehaus et al.208-203 2,752,290 6/1956 Beattie 20440l 3,108,935 10/1963 Penning et al.208-97 3,140,248 7/1964 Bell et al. 20840 FOREIGN PATENTS 627,307 9/1961Canada. 783,567 9/1957 Great Britain.

OTHER REFERENCES The Chemical Technology of Petroleum, W. A. Gruse andD. R. Stevens, Second edition (1942), pages 405-406, McGraw-Hill BookCo., New York.

DANIEL E. WYMAN, Primary Examiner.

P. E. KONOPKA, Assistant Examiner.

